Proposed approach for reusing surgical masks in COVID-19 pandemic

Graphical abstract

To the Editor: Coronavirus disease 2019 (COVID-19) is a novel human respiratory disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. Washing hands and social distancing are measures recommended by the Centers for Disease Control and Prevention to prevent COVID-19 transmission. However, new evidence shows that the half-life of viable SARS-CoV-2 in aerosol is longer than 1 hour, indicating a high likelihood of airborne transmission.¹ Furthermore, the existence of an asymptomatic carrier phase decreases the effectiveness of prevention strategies that rely on symptoms.

There is a strong rationale for a universal mask policy. Wearing a face mask will not only prevent airborne viral transmission but also reduce the likelihood of one's hands touching the mouth and nose. It is particularly needed to prevent the transmission from asymptomatic medical professionals to patients and colleagues. Owing to the current shortage of masks, it is prudent to conserve masks whenever possible. More than 100 billion masks will be needed for 300 million Americans annually if 1 person uses 1 mask per day. This is far beyond the current capacity of United States face mask manufacturing.

Although the United States Food and Drug Administration has approved mask decontamination by H₂O₂ vapor, it requires special equipment that limits its widespread application. A simple, effective decontamination method that does not disrupt filtration efficacy of the mask is needed.

Decontamination of masks is challenging because the filtration capacity of polypropylene is vulnerable to most commonly used sterilization methods, including autoclaving, bleach, and alcohol.² The filtration layer of masks is made of melt-blown polypropylene that determines the pore size of a face mask. An analysis of 5 different decontamination methods identified dry heat as a preferred method.² Although the dry heat approach did not significantly change the filtration efficiency of melt-blown polypropylene, it forms crystals at higher temperatures.³ The accumulation of the crystals will ultimately compromise the filtration efficiency.

On the basis of the low crystallinity of polypropylene at 70°C³ and data demonstrating that coronavirus can be effectively inactivated at 65°C for 30 minutes,⁴ dry heat at 65° to 70°C for 30 min should be an effective condition to decontaminate used masks. It has been demonstrated that the filtration efficiency of a face mask is not significantly changed after up to 20 cycles of decontamination with hot air (75°C) for 30 minutes in each cycle.⁵

Heating at 65° to 70°C can be achieved by baking in an oven, incubator, or even a blanket warmer. Although the efficiency of a mask treated under these conditions remains to be determined, this method provides a simple, straightforward, and effective strategy for decontamination of used masks. The general guideline for reuse of face masks includes:

• 1.Masks contaminated with fluids should not be reused, due to the compromise of filtration efficiency.
• 2.When sanitizing with heat, place the mask in a brown paper bag, with your name on it, to avoid direct contact with the metal surface or other masks.
• 3.The 0.3- to 10-μm pore size of standard surgical face masks is much larger than the coronavirus (0.1 μm) and incompletely form-fits the face. Therefore, surgical masks should not be used when in contact with patients that are potentially positive for COVID-19.